1. Field of the Invention
The invention relates in general to a material feed system for solid freeform fabrication and, in particular, to a quantized feed system that can selectively feed discrete portions of material directly to a solid freeform fabrication device to build three-dimensional objects. Because the feed system is quantized, the system can be used to build three-dimensional objects in color or to dispense more than one material. In addition, the feed system can be integrated with a hermetically sealed waste removal system wherein reactive materials can be handled without special handling procedures.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as solid freeform fabrication, herein referred to as “SFF”. Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. In SFF, complex parts are produced from a modeling material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, typically layer by layer, in order to build a complex part.
SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers. SFF technologies have many advantages over the prior conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can quickly produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with the prior conventional manufacturing methods, particularly when creating molds for casting operations. In addition, SFF technologies are advantageous because customized objects can be produced quickly by processing computer graphic data.
There are a wide variety of build materials that are used in various SFF techniques. These materials are typically applied in the form of a powder, liquid, gas, paste, foam, or gel. Recently, there has developed an interest in utilizing highly viscous paste materials in SFF processes to achieve greater mechanical properties. In addition, an interest has recently developed in reproducing visual features such as color on the three-dimensional objects produced by SFF processes. This has produced a need to develop special additives for the build materials along with new dispensing systems to enable the production of these visual features when building the three-dimensional objects.
One category of SFF that has emerged is selective deposition modeling, herein referred to as “SDM”. In SDM, a build material is physically deposited in a layerwise fashion while in a flowable state and allowed to solidify to form an object. In one type of SDM technology the modeling material is extruded as a continuous filament through a resistively heated nozzle. In yet another type of SDM technology the modeling material is jetted or dropped in discrete droplets in order to build up a part. In one particular SDM apparatus, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as those used in ink jet printers. One type of SDM process utilizing ink jet print heads is described, for example, in U.S. Pat. No. 5,555,176 to Menhennett, et al.
Because ink jet print heads are designed for use in two-dimensional printing, special modifications must be made in order to use them in building three-dimensional objects by SFF techniques. This is generally because there are substantial differences between the two processes requiring different solutions to different problems. For example, in two-dimensional printing a relatively small amount of a liquid solution is jetted and allowed to dry or solidify with a significant interest being given to print resolution. Because only a small amount of material is jetted in two-dimensional printing, the material reservoir for the liquid solution can reside directly in the ink jet print head while providing the ability to print numerous pages before needing to be refilled or replaced. In contrast, in SDM a normally solid material, such as a thermoplastic or wax material, must be heated to a flowable state in order to be jetted, and then allowed to solidify. Furthermore, in SDM dispensing resolution is not as critical as it is in two-dimensional printing. This is generally because, for each targeted pixel location, the amount of material to be jetted in SDM techniques is substantially greater than the amount to be jetted in two-dimensional printing techniques. For example, it may be required to deposit six droplets on a particular pixel location in SDM compared to just one or two droplets in two-dimensional printing. Although the targeting accuracy may be the same, the actual resolution achieved in SDM techniques is generally somewhat less than in two-dimensional printing because the six droplets dispensed may droop or slide towards adjacent pixel locations.
Another difference is that because of the substantially greater amount of material jetted in SDM, the rate at which objects are formed becomes important. Since achieving higher build rates in SDM has been a high priority, initial SDM techniques dedicated all the discharge orifices in the ink jet print heads to dispense a single build material to maximize the build rate of forming the three-dimensional object. However, this sacrifices the ability to selectively dispense multiple colors from the print head when forming the object.
The differences mentioned above are significant and create a number of problems to be resolved. For instance, the amount of material deposited in SDM techniques, both in volume and in mass, can be so substantial that it is generally considered impractical to mount a reservoir directly on die ink jet print head to hold all of the material. Thus, it is typical in most SDM systems to provide a large reservoir at a remote location from the print bead that is in communication with the ink jet print head via a material delivery system having a flexible umbilical cord. However, the large container and umbilical cord must be heated to cause at least some of the build material to become or remain flowable so that the material can flow to the dispensing device. Undesirably, start up times are longer for SDM techniques using ink jet print heads than in two-dimensional printing with ink jet print heads due to the length of time necessary to initially heat the solidified material in the large remote reservoir to its flowable state. In addition, a significant amount of energy is required to maintain the large quantity of material in the flowable state in the reservoir and in the delivery system during the build process. This undesirably generates a significant amount of heat in the build environment.
As higher build speeds have been a priority in SDM techniques, previous expedients have abandoned the color dispensing capabilities of the ink jet print heads and have instead dedicated all of the dispensing orifices of the print heads to dispensing a single build material provided from a single large reservoir. According to these prior art delivery systems multiple remote reservoirs and delivery systems would be necessary in order to dispense multiple materials to produce multiple colors in an object. This would multiply the complexity and cost of such a system and is generally not practical. Thus, there is a need to overcome the limitations of the prior art SFF feed systems that utilize a remotely heated material reservoir. There is also a need to develop a feed system for an ink jet print head used in SFF that can take advantage of the color dispensing capabilities of the print heads.
Previous expedients have been proposed for delivering a phase change ink to a print head for two dimensional printing. For example, in U.S. Pat. No. 5,861,903 to Crawford et al., a supply of ink sticks or blocks are linearly stacked in a loading bin that biases the stick at the end of the stack against a melt plate and the melted ink then drips into the print head in a liquid state. Similarly in U.S. Pat. No. 4,593,292 to Lewis and in U.S. Pat. No. 4,609,924 to De Young, a long block of solid ink is biased against a heater plate to melt the ink for delivery of the melted ink to a print head. Also, in U.S. Pat. No. 4,636,803 a supply of cylindrical pellets of solid ink are advanced along an elongated array prior to being melted for use by an ink jet print head. In U.S. Pat. No. 4,631,557 to Cook et al., a cartridge holding a phase change material is heated to allow the melted material to drain into a supply system for a print head. In U.S. Pat. No. 4,682,185 to Martner, a flexible web of hot melt ink is advanced on a spool to a heater where the material is then melted prior to delivery to a ink jet print head. In U.S. Pat. No. 5,341,164 to Miyazawa et al., a number of embodiments of an ink jet supply system are disclosed. In one embodiment an elongated array of solid ink is advanced and broken off at cutouts prior to being melted. In another embodiment, a vertical array of solid spheres of ink are held in single file and are selectively dropped into the print head. However, these prior expedients are directed to feed systems for two-dimensional printing and do not address the problems confronted in SDM techniques, such as how to handle and deliver the significantly larger quantity of build material needed to form three-dimensional objects. For example, the prior linear or array feed systems, if used for SDM, would have to be extremely long in order to hold the quantity of material needed, or require constant manual refilling during the build process. Neither of these alternatives are desirable in SDM.
Another problem that is unique to SDM techniques is that the layers being formed must be shaped or smoothed during the build process to establish a uniform layer. Normalizing the layers is commonly accomplished with a planarizer that removes a portion of the material dispensed in the layers. One such planarizer is disclosed in U.S. Pat. No. 6,270,335 to Leyden et al. However, the planarizer produces waste material during the build process that must be handled. Normally this is not a concern when working with non-reactive materials; however, it can become a problem when reactive materials are used. For example, most photopolymers are reactive, and excessive contact to human skin may result in sensitivity reactions. Thus, most all SFF processes that utilize photopolymer materials require some additional handling procedures in order to minimize or eliminate excessive physical contact with the materials. For example, in stereolithography, operators typically wear gloves when handling the liquid resin and when removing finished parts from the build platform. However, SDM operators who normally handle non-reactive materials consider additional handling procedures inconvenient and, if possible, would prefer they be eliminated. Thus, there is a need to provide a material feed and waste system for SDM that can handle reactive materials without requiring the implementation of special handling procedures.
These and other difficulties of the prior art are overcome according to the present invention by providing build material to the dispensing device of a SFF apparatus in discrete portions on an as needed basis when the apparatus is forming a three-dimensional object.